The present application relates to solid storage media for ammonia, and more particularly, but not exclusively, to methods and systems for charging of solid storage media with ammonia for use in selective catalytic reduction.
Solid materials for ammonia storage have been developed as a source of reductant in selective catalytic reduction (SCR). By dosing gaseous ammonia from solid storage media, the SCR system is capable of working at temperatures below the current limits of traditional urea-based SCR systems. Solid media storage systems for ammonia also operate without the negative aspects associated with urea-derived deposit problems in the exhaust system.
Current solid media storage systems for ammonia are primarily based on using inorganic salts including alkaline-earth metal chloride salts, such as SrCl2 or MgCl2, as a storage media to absorb and release ammonia. The storage media is charged with ammonia by exposing the storage media in powder form to gaseous ammonia to slowly saturate the salts, and then compressing the saturated salts into high-density storage media elements. In use, the solid storage media is placed in cartridges mounted in the exhaust system and the ammonia is released by applying heat to the storage media in the cartridge.
Absorption of ammonia in metal chloride salts is a highly exothermic process. For example, in the case of SrCl2, the process produces 41 kJ/mol of stored ammonia (SAE 2009-01-0907). This amounts to a very large (thousands ° C.) temperature increase unless the evolving heat is removed from the storage media or compensated by another endothermic process. When the storage media is spent of ammonia, charging of the storage media is accomplished by saturation of the spent storage media using liquid anhydrous ammonia such that the heat required for ammonia vaporization would, to some degree, offset the heat produced by the ammonia reaction with the storage media. However, large amounts of heat are still generated. Thus, the charging process is accomplished by removing the spent storage media elements and/or the cartridge of spent elements from their application and processing them at a remote location due to safety and handling concerns for the liquid ammonia. Spent cartridges may also be removed and rebuilt using new or recycled storage media.
These re-charging options for spent cartridges have limited viability due to the heat that is generated and the complexity and cost associated with handling anhydrous ammonia. Furthermore, the cost associated with re-building cartridges with new or recycled storage media can be relatively high. Without the capability to re-charge the storage media inexpensively and/or at a dealership or service center, the economic viability of the solid storage media technology for ammonia may be limited. Thus, there remains a need for further contributions in this area of technology.